After a well has been drilled such as for production of petroleum products, a tubing string is inserted through the well bore established by the casing and is secured by means of a surface hanger assembly. The formation level of the well is isolated from the annulus between the tubing and casing by means of appropriate packer devices. It is frequently necessary to conduct inspection and servicing activities for protection of the well and for enhancing its production and service life. For example, inspection of formation pressure is necessary on a regular basis in order to determine the continuing status of the formation and thus permit maximized production from the well. It is impractical to check formation pressure at the surface and it is also risky to inspect formation pressure under flowing conditions. Formation pressure is typically inspected by postioning a pressure detection instrument in the tubing string near the formation level and temporarily shutting in the well to cease production activity while this temporary inspection is being conducted.
Obviously, when pressure measurement equipment is located in the flow passage of the well, it is subject to a pressure differential established by formation pressure and the tubing pressure above the pressure measuring instrument. When temporarily installed pressure measurement tools are employed it is possible for them to be ejected from the well by formation pressure and it is not usually possible to achieve max production flow with typical pressure measurement tools in place.
In every case when measuring bottom hole pressure, it is desirable to close off the tubing string above the pressure measurement recorder and as near to the formation level as possible. This will eliminate the storage effect, i.e., the effect of the formation filling the production string all the way to the surface and then effecting a maximum buildup of pressure. In some cases this process can take days or even weeks when formations are very tight. This is very costly when a rig is on location because of the per dium expense of the rig and the cost of labor. Until recently, a mechanical recorder would be used below a plug assembly which is positioned by wire-line equipment and which would be lowered into the well bore and locked into a nipple recess near the level of the formation. At some later point in time the plug and recorder would be retrieved by wireline methods. If for some reasons the recorder failed to work properly it is necessary to repeat the entire process. According to the present state of technology it is possible to record bottom hole pressure at the formation level by using an electronic instrument which records pressure and temperature and sends this information to a computer at the surface by way of electronic pulses traveling along a conductor wire-line. Because this instrument is connected to surface equipment by a wire-line it is not possible to set a plug above the equipment. Therefore, a plug must be set below the instrument and, a way must be devised to monitor the formation pressure below the plug by utilizing a bypass device that can be opened and closed by pulling or slackening the wire-line from the surface. The present invention effectively accomplishes these features.